Claims that witnesses face a campaign of intimidation and are too frightened to give evidence at a Birmingham election court are to be investigated by the Director of Public Prosecutions.

The DPP was called in after a judge was told Liberal Democrat supporters had been warned not to turn up at the court, which is hearing details of an alleged Labour smear campaign at the 2007 city council election in Aston.

The court is considering an election petition brought by Liberal Democrat candidate Saeed Aehmed, who claims he lost the election to Labour councillor Muhammad Afzal by more than 600 votes as a result of false statements issued by Coun Afzal and his family.

It is alleged Coun Afzal and Labour supporters told people at polling stations not to vote for Mr Aehmed because he had been arrested for postal vote fraud and had fiddled disability benefits - both claims were untrue.

Recorder Timothy Straker QC, sitting as the Elections Commissioner, ordered counsel for the DPP to attend all further sessions of the court, which is due to resume sitting on December 4.

The decision followed the appearance in the public gallery last Friday of two Labour supporters while the court was hearing evidence from Lib Dem supporter Mukhtar Ahmed.

Fatima Patwa, solicitor for the petitioners, said the two had visited the witness the night before at his home in an attempt to persuade him not to give evidence.

Ms Patwa added that two other witnesses were refusing to come to court, claiming to be sick.

"We have our suspicions about that," she added.

Ms Patwa said: "Another witness has written a letter saying he is withdrawing his statement. His cars have been smashed and he is leaving Birmingham for his own safety. This is becoming serious."

Ayoub Khan, a Liberal Democrat Aston councillor and Birmingham cabinet member, who has already given evidence in the case, said: "There is clearly a campaign of intimidation going on."

Coun Afzal and the Labour Party deny all of the allegations in the election petition.